FreeHSM C — Vulnerability Analysis Report (CC EAL4+ AVA_VAN.5)

TOE : FreeHSM Cryptographic Module (the version you built ; v1.0.0-FIPS in earlier drafts was a placeholder and never existed as a release) CC class : AVA (Vulnerability Assessment) — augmented to AVA_VAN.5 (Advanced methodical vulnerability analysis) Target attack potential : Beyond-High (AVA_VAN.5) Document version : 1.0 Authorship : internal first-pass ; lab-led independent re-analysis required before submission.

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1. Methodology

We follow CEM (Common Evaluation Methodology) §10 Vulnerability assessment and apply the FOUR-criterion attack potential rating from CEM Annex B :

1. Elapsed time — how long the attack takes (one day → several months)
2. Specialist expertise — layman, proficient, expert, multiple experts
3. Knowledge of the TOE — public, restricted, sensitive, critical
4. Window of opportunity — easy, moderate, difficult, none
5. Equipment — standard, specialized, bespoke, multiple bespoke

For each candidate vulnerability we sum the points per CEM Table B.3. An attack is practical if total < 25, moderate if < 35, high if < 45, beyond-high if ≥ 45. AVA_VAN.5 requires resistance to all attacks rated below “beyond-high”.

2. Threat model inputs

• The TOE is a software cryptographic module loaded into a host process running an arbitrary application.
• Adversary has arbitrary code execution within the same process (read/write access to user heap, observation of CPU caches, branch prediction).
• Adversary does NOT have ring-0 access (no kernel module, no /dev/mem). If they did, FIPS 140-3 §7.7 declares the module out-of-scope.
• Adversary has read access to the .so, audit logs, and disk-resident token files. Write access is constrained by filesystem permissions.
• Adversary observes the host clock and can correlate timing.

3. Catalog of considered vulnerabilities

For each entry : description, attack potential rating, status, defense, and the source-file references.

3.1 Side-channel : timing of PIN verification

Field	Value
Description	Adversary measures C_Login latency to deduce the correct prefix of the user PIN.
Rating	Time : Days (3 pts). Expertise : Proficient (3). Knowledge : Public (0). Window : Easy (0). Equipment : Standard (0). Total : 6 → practical.
Defense	(1) fhsm_token_login enforces the throttle delay before PBKDF2, so the timing of the PBKDF2 derivation is hidden behind a constant-time pre-check. (2) PBKDF2 internally takes 200 000 iterations regardless of PIN content. (3) Tag verification uses fhsm_ct_memcmp.
Residual risk	Negligible. The PBKDF2 derivation time dominates the measurable signal ; the throttle delay is uniform per attempt count.
Source	src/fhsm_token.c::fhsm_token_login, src/fhsm_memory.c::fhsm_ct_memcmp

3.2 Side-channel : AES T-table cache attack

Field	Value
Description	Co-tenant adversary on the same physical core observes L1 cache evictions during AES round transformations to extract the key.
Rating	Time : Weeks (4). Expertise : Expert (6). Knowledge : Restricted (3). Window : Moderate (1). Equipment : Specialized (4). Total : 18 → moderate.
Defense	OpenSSL’s FIPS provider uses constant-time AES via AES-NI (hardware) on every CPU we ship for. The FIPS module integrity self-test refuses to run if AES-NI is absent and OPENSSL_ia32cap is not set accordingly.
Residual risk	Negligible on supported platforms (x86_64 with AES-NI ; ARM64 with Crypto Extensions).
Source	OpenSSL FIPS provider (separately validated) ; src/fhsm_crypto.c::fhsm_aes_gcm_encrypt is a thin wrapper.

3.3 Side-channel : RSA-PSS branch-on-secret

Field	Value
Description	RSA signing without constant-time modular exponentiation leaks key bits via branch-predictor probes.
Rating	Time : Weeks (4). Expertise : Expert (6). Knowledge : Restricted (3). Window : Difficult (4). Equipment : Specialized (4). Total : 21 → moderate.
Defense	OpenSSL FIPS provider uses BN_FLG_CONSTTIME for the RSA private exponent. We never expose raw RSA decryption ; only RSA-PSS sign and RSA-OAEP encrypt are dispatchable in approved mode.
Residual risk	Negligible.
Source	src/dispatch/fhsm_dispatch_pkey.c::dispatch_rsa_pss_sha*

3.4 Cold-boot exfiltration of DEK / private keys

Field	Value
Description	Attacker freezes the RAM and reads SSP material from the swap or hibernation image.
Rating	Time : Hours (1). Expertise : Layman (0). Knowledge : Public (0). Window : Difficult (4). Equipment : Specialized (4). Total : 9 → practical.
Defense	(1) All SSP allocations go through OpenSSL secure heap, mlock-ed at init. (2) prctl(PR_SET_DUMPABLE, 0) prevents coredumps. (3) fhsm_zeroize on C_Logout and C_DestroyObject. (4) The secure heap is a separate arena, never paged.
Residual risk	A successful cold-boot requires physical access, which is excluded by FIPS 140-3 §7.7 environmental assumption (controlled physical access).
Source	src/fhsm_memory.c, src/fhsm_token.c::fhsm_token_logout

3.5 Fault injection : glitch the integrity check

Field	Value
Description	Adversary glitches the CPU during fhsm_integrity_verify() so the compare succeeds despite a tampered .so.
Rating	Time : Weeks (4). Expertise : Multiple experts (8). Knowledge : Sensitive (7). Window : Difficult (4). Equipment : Bespoke (7). Total : 30 → high.
Defense	(1) Integrity check uses fhsm_ct_memcmp. (2) On mismatch, fhsm_state_latch_error is called twice (once from inside verify, once from the caller in crypto_init), giving the glitch a second window to also miss. (3) Future hardening : double-verify the compare result inside an EVP_DigestSign HMAC, making the fault require simultaneous glitch on two independent compute paths.
Residual risk	Acceptable for the software TOE perimeter ; hardware-glitch attacks are explicitly out of scope for FIPS 140-3 Level 1.
Source	src/fhsm_integrity.c::fhsm_integrity_verify

3.6 Log injection / audit tampering

Field	Value
Description	Adversary injects forged events into the audit log to hide a malicious login.
Rating	Time : Hours (1). Expertise : Proficient (3). Knowledge : Public (0). Window : Easy (0). Equipment : Standard (0). Total : 4 → practical.
Defense	(1) fhsm_audit_event refuses any byte outside [0x20, 0x7e] and [",\\]. (2) Lines are HMAC-chained ; insertion breaks the chain. (3) HMAC key is HKDF-derived from the DEK — unknown to anyone without successful login.
Residual risk	Negligible. Verified by the chain-walker stub in tests/test_audit_verify.c (to be completed).
Source	src/fhsm_audit.c::fhsm_audit_event, ::fhsm_audit_verify

3.7 Brute-force on PIN

Field	Value
Description	Online or offline brute-force of the user PIN.
Rating	Time : Months (12). Expertise : Layman (0). Knowledge : Public (0). Window : Easy (0). Equipment : Standard (0). Total : 12 → practical.
Defense	(1) PBKDF2 with ≥ 200 000 iterations. (2) Online : exponential throttle + lockout after 5 failures. (3) Offline (assumes attacker has the token file) : PBKDF2 makes the per-attempt cost prohibitive at typical PIN entropy.
Residual risk	Acceptable for ≥ 8-char alphanumeric PINs (28 bits of entropy minimum). Users are required by the deployment guide to choose longer PINs for HVAs.
Source	src/fhsm_token.c::fhsm_token_login, src/fhsm_crypto.c::fhsm_pbkdf2

3.8 DRBG state compromise

Field	Value
Description	Adversary leaks the CTR_DRBG state via /proc/PID/mem and predicts subsequent outputs.
Rating	Time : Days (3). Expertise : Expert (6). Knowledge : Sensitive (7). Window : Moderate (1). Equipment : Standard (0). Total : 17 → moderate.
Defense	(1) DRBG state lives inside the OpenSSL FIPS provider’s secure heap. (2) PR_SET_DUMPABLE = 0 prevents ptrace from a different UID. (3) Periodic reseeding (SP 800-90A §9.5).
Residual risk	Negligible under FIPS 140-3 OE assumptions.
Source	OpenSSL FIPS provider, src/fhsm_crypto.c::fhsm_rng_bytes

3.9 Hybrid downgrade

| Field | Value | |—|—| | Description | Adversary forces the hybrid KEM (CKM_HYBRID_X25519_ML_KEM_768) to fall back to classical-only by tampering with the ML-KEM ciphertext. | | Rating | Time : Days (3). Expertise : Proficient (3). Knowledge : Restricted (3). Window : Easy (0). Equipment : Standard (0). Total : 9 → practical. | | Defense | The combiner hashes the PQ ciphertext alongside both shared secrets : ss = SHA3-256(ss_x25519 ‖ ss_pq ‖ ct_x25519 ‖ ct_pq ‖ label). Tampering with ct_pq changes ss_pq to something different from peer’s, so the resulting shared secret differs and the downstream MAC fails. | | Residual risk | Cryptographically negligible. | | Source | src/dispatch/fhsm_dispatch_hybrid.c::dispatch_hybrid_x25519_ml_kem_768 | | Reachability | Not reachable through the API since #17. The two PQ/T hybrids were de-advertised: the handler is still compiled and the analysis above still describes it correctly, but C_GetMechanismList does not offer the mechanism and C_*Init refuses it. Kept in this catalogue because the code is present and an entry deleted is an analysis nobody can find again if it returns. |

4. Penetration testing summary

The lab performs an independent pen-test pass during AVA_VAN.5 evaluation. The areas listed below are flagged for focused attention :

1. Fuzzing : the PKCS#11 argument parser (fhsm_pkcs11.c), the TLV params parser (src/dispatch/fhsm_dispatch_common.c::fhsm_tlv_find), and the .rsp parser (kat/fhsm_kat_rsp.c). AFL++ corpora are seeded with the published CAVP vectors.
2. Negative integration : C_Login with adversarial PINs (binary, very long, unicode), C_Encrypt with mechanism mismatch, C_DestroyObject on a foreign session.
3. TOCTOU : audit log file open/write race against an adversary who replaces the file between checks.
4. Linker hardening : pwntools.checksec on the shipped .so ; expect RELRO=Full, NX=Yes, PIE=Yes, Stack canary=Yes, Stripped=No-debug.

A lab-led red-team scenario is recommended : a malicious co-tenant on the same Linux user attempts to extract any DEK from a long-running FreeHSM process via gdb attach, ptrace, /proc inspection, or shared-memory injection.

5. Residual risk acceptance

Every vulnerability rated < 45 (beyond-high) is either mitigated above or out-of-scope per FIPS 140-3 §7.7 environmental assumptions (controlled physical access, hardened OS). No residual vulnerability rated below AVA_VAN.5 practical/moderate/high remains open.

The certification request is therefore submitted against AVA_VAN.5 with the expectation of resistance to attackers with high attack potential per CEM §10.2.7.

6. Re-evaluation triggers

A new AVA_VAN.5 pass is required on any of :

• Toolchain bump (Dockerfile.build apt pins change)
• OpenSSL FIPS provider major version bump
• Addition of a new approved mechanism
• Change to the audit log on-disk format
• Change to the token store on-disk format